The 1,2,3,4,6,7,12,12b-octahydroindolo[2,3-a]-quinolizin-1-yl-alkanecarboxylic acid amide derivatives of the formula (I) according to the invention are new. There are some compounds known from the literature which are structurally related substances (Belgian patent specification No. 872,134; CA 91, 39454e; U.S. Pat. No. 4,353,911), wherein the substituted acid amide moiety is directly (i.e. without the interruption through an alkylidene chain) connected with the carbon atom in position 1 of the indolo[2,3-a]-quinolizine skeleton.